By excluding languages like Scheme, and many others, they are excluding developers who prefer these languages. One could argue that these developers are among the smarter and more creative ones. So, when competitors get their act together, and come out with a similar device that doesn't suck, and an app store alternative that does not have these restrictions, then this is where such developers will go.
Essentially, they're providing the competition with a sizable pool of (often disgruntled) developers. There is no real competition right now, but they're making it more likely that there will be, in a year or two.
Anyway, just my $0.99... :-)
Again, as much as I'd like to agree with you, none of the prominent app developers are going to be leaving anytime soon. And, as for people who make Farting apps, they probably wont care anyways because use Objective-C or Actionscript, the apps are rather simple anyways. The efficiency of writing code probably wont matter to them.
They certainly won't start whining about it.
Awesome thing is, though, that you can reasonably compete as a Tier C developer with Tier B and Tier A developers, it's just that they get a head start with being featured. That's surmountable, so it's not a big deal.
They're a business.
For every clojure zealot, there are probably 10 objective-c developers who will be happy with less competition.